1. Technical Field
The present invention relates to a quantum interference device, an atomic oscillator, an electronic apparatus, and a moving object.
2. Related Art
As for an oscillator which has a high accuracy oscillation characteristic for a long period of time, an atomic oscillator is known which oscillates on the basis of energy transition of atoms of an alkali metal such as rubidium or cesium.
Generally, operation principles of the atomic oscillator are largely classified into a method of using a double resonance phenomenon caused by light and microwaves, and a method of using a quantum interference effect (also referred to as coherent population trapping (CPT)) caused by two types of light beams with different wavelengths.
In an atomic oscillator of either method, an alkali metal is sealed into a gas cell along with buffer gases, and the gas cell is required to be heated to a predetermined temperature by a heater in order to maintain the alkali metal in a specific gaseous phase.
Here, generally, the entire alkali metal in the gas cell does not become a gas, and part of the alkali metal becomes a liquid as a surplus. Such surplus alkali metal atoms are deposited (condensed) at a location of the gas cell where a temperature is low and thus become a liquid, but if the liquid of the surplus alkali metal atoms is present in a passing region of the excitation light to shield the excitation light, as a result, an oscillation characteristic of the atomic oscillator deteriorates.
Therefore, in a gas cell disclosed in JP-A-2007-324818, a recess for depositing an alkali metal is provided at a position which is deviated from an optical axis of excitation light. Apart which is separated from the recess of the gas cell is heated by a heater, and thus a temperature of the recess is made lower than that of a peripheral portion. Thus, a surplus of the alkali metal is reserved in the recess as a liquid, so that the surplus is prevented from shielding the excitation light.
However, in a case where an atomic oscillator disclosed in JP-A-2007-324818 is miniaturized, heat generated from the heater is transmitted to the entire atomic oscillator depending on its size. For this reason, a temperature of the recess also increases. As a result, there is a possibility that the surplus of the alkali metal may not be reserved in the recess as a liquid and thus the surplus may shield the excitation light. As mentioned above, it is difficult to partially change a temperature of the gas cell of the miniaturized atomic oscillator.